TiO2 Photocatalytic Degradation of Dichloromethane:  An FTIR and Solid-State NMR Study

The photocatalyic oxidation of dichloromethane over TiO2 was studied using in situ FTIR and solid-state NMR (SSNMR) methods. Dichloromethane photodegradation led to the formation of a number of long-lived intermediate species including CO, HCl, phosgene, chloroform, and CCl4 in the presence of oxygen. FTIR studies showed that the reaction rate and product distribution were strongly dependent on the oxygen concentration. Species often thought to be products in the reactions, particularly HCl, CO, and CCl4, were found to degrade to CO2 and H2O under high relative oxygen concentrations. In addition, formyl chloride was identified as a new intermediate, while phosgene was found to have two production channels. SSNMR experiments showed that one of the two phosgene species resides primarily in the gas phase, while the other was associated with the surface. Additional SSNMR studies of the adsorption of dichloromethane showed that a chloromethoxyl species was formed on anatase TiO2. SSNMR experiments were also helpful in quantifying the intermediates and products.